This invention relates to brake pressure control valves for use in dual-circuit brake systems in vehicles such as automobiles.
Brake pressure control valves adapted for use in a dual-circuit brake system of X-type connection wherein the righthand front wheel brake and the left-hand rear wheel brake constitute one of the circuits and the left-hand front wheel brake and the right-hand rear wheel brake constitute the other circuit are, as shown in U.S. Pat. No. 3,969,000 or the like, known to the public. The brake pressure control valves shown in the above patent have the characterizing feature that two valve bodies separately receiving hydraulic pressure in respective circuits are controlled by a single spring such that when the hydraulic pressures in the respective circuits are normal the valve bodies move toward one another by compressing the spring to control the rear wheel brakes at a predetermined pressure. However, when one of the hydraulic pressure circuit fails the valve body in the failed circuit does not move so that the spring is not correspondingly compressed thus reducing the spring force acting on the valve body in the other circuit and reducing the hydraulic pressure in the rear wheel brake of the other circuit.
Further, there is a necessity to increase the hydraulic pressure in the rear wheel brake for maintaining the overall braking effect when failure occurs in one of the circuits, since the available hydraulic circuits are reduced to half.